Five isolates, Sphingomonas sp. strain O12, Sphingomonas sp. strain A32, Sphingomonas

sp. strain A55, Stenotrophomonas sp. strain C21 and Arthrobacter sp. strain O4, were resistant to high Cu2+ concentration (≥ 2.8 mM) and other heavy metals. Bacteria that tolerate Cu concentrations higher than 2 mM should possess an effective resistance system for Cu detoxification. The isolates Sphingomonas sp. strain O12, Sphingomonas sp. strain A32 and Sphingomonas sp. strain A55, showed a high MIC to Cu2+ (ranged from 3.9 to 4.7 mM), Co2+ (2.5 mM), Ni2+ (17 mM), Zn2+ (8.5 mM) and Hg2+ (0.4 mM) (Table 2). The MIC of the heavy metal Selleckchem Dabrafenib resistant bacterium C. metallidurans strain MSR33 to Cu2+, Co2+, Ni2+, Zn2+ and Hg2+ is 3.8, 20, 6.0, 17 and 0.1 mM, respectively. Stenotrophomonas learn more sp. strain C21 and Arthrobacter sp. strain O4 showed a high MIC to Cu2+ (ranged from 3.1 to 3.9 mM) and CrO4 2- (4.3 mM). C. metallidurans strain MSR33 has a MIC to CrO4 2- of 0.7 mM. These high levels of heavy metal resistances may be useful for surviving and adapting to acute heavy metal contamination events in the soil. The mechanisms involved in heavy metal resistance of the strains isolated should be studied. Sphingomonas macrogoltabidus strain S1n isolated from rhizosphere of Alyssum murale, showed a high MIC to Cu2+ (5

mM) and Ni2+ (15 mM) [38]. Stenotrophomonas maltophilia strain SM777 isolated from a contaminated culture, showed high MIC to Cu2+ (5 mM), Ni2+ (10 mM), Zn2+ (4 mM), and Hg2+ (0.05 mM) [39]. Arthrobacter sp. strain E9 isolated from a battery-manufacturing contaminated site, showed a high MIC to Cu2+ (5.8 mM), Co2+ (2.5 mM), Zn2+ (3 mM) and Hg2+ (0.06 mM) [40]. Arthrobacter sp. strain S189 isolated from rhizosphere of Alyssum murale, showed a high MIC to Cu2+ (10 mM), Co2+ (5 mM), Ni2+ (15 mM), Zn2+ (10 mM) and Hg2+ (0.5 mM)

[38]. Nintedanib (BIBF 1120) The high level of heavy metal resistance of Sphingomonas sp. strain O12, Sphingomonas sp. strain A32, Sphingomonas sp. strain A55, Stenotrophomonas sp. strain C21 and Arthrobacter sp. strain O4 suggests that these strains possess diverse heavy metal determinants. The use of specific primers based on heavy metal determinants from C. metallidurans strain MSR33 did not yield amplicons. In future studies, the presence of heavy metal resistance genes will be studied using more general primers. In this study, the presence of multi-copper oxidase gene was evaluated in the five isolates using degenerated primers designed for copA sequences from Proteobacteria. The presence of multi-copper oxidase copA genes in both Gram-negative and Gram-positive bacteria was determined. The presence of copA gene in both bacterial groups suggests that the cop system involved in Cu-resistance could be widespread in soil probably through horizontal genes transfer among soil bacteria.